Function capture argument evaluation

[jrunning]

I have this code from an Exercism exercise:

pub fn is_pangram(sentence: String) -> Bool {
  "abcdefghijklmnopqrstuvwxyz"
  |> string.to_graphemes
  |> list.all(fn(letter) {
    string.contains(string.lowercase(sentence), letter)
  })
}

In this code, I know that string.lowercase(sentence) will be called 26 times, once for each iteration of list.all. That's not very efficient* and it would be smarter to do that work outside the callback.

Now, suppose I replace that anonymous function with a function capture:

pub fn is_pangram(sentence: String) -> Bool {
  "abcdefghijklmnopqrstuvwxyz"
  |> string.to_graphemes
  |> list.all(string.contains(string.lowercase(sentence), _))
}

In this case, will string.lowercase(sentence) be called 26 times, or just once? I'm guessing it's the former, and that function capture is just syntax sugar, but the docs call it "a shorthand syntax" which gives me less certainty.

*I realize this could be optimized by the runtime, but this is just a trivial example.

[GearsDatapacks]

The two examples compile to the exact same code (with the exception of different variable names), so yes 26 times for both.
If you only want to call it once, you should declare a variable beforehand